Every society's holiest duty is ensuring that all its children thrive to the greatest extent possible. But while almost everyone will agree in a bland way that it's important to care for our children, it's striking how little our kids feature in our national political debates.

What helps children thrive? When it comes to answering this question, we can — and must — disagree in good faith.

But there is an emerging scientific consensus about a few things that, regardless of how you feel or what you believe, really do help children thrive, and one of them is family stability. A growing body of sociological findings strongly suggest that family instability has negative effects on children reaching well into adulthood, from perceived well-being to educational attainment to income.

One of the report's key findings? A link between cohabitation — when two unmarried people live together — and family instability.

This is highly interesting. A common refrain when discussing family instability is that parents' education and economic status is the most important criterion for family instability. Poorer and less educated parents are more likely to break up, and wealthier and more educated parents more likely to stay together. The implication is that to promote stable families, policies should focus on economic and social aid, rather than on trying to strengthen the institution of marriage.

Indeed, we typically read about how well-to-do cohabiting families in places like Sweden and France are just as stable as any other. During the 2007 French presidential election, left-of-center American publications gushed about the fact that the Socialist presidential candidate, Ségolène Royal, was cohabiting with her partner, François Hollande (who would go on to run as well, and be elected to the presidency), with whom she raised four children. They were mostly silent when the couple announced their breakup right after the election.

This new research finds that children born to cohabiting couples in the United States and Europe are much more likely to see their parents break up before they turn 12 than are children born to married couples. Indeed, in 17 European countries and in the United States, highly educated cohabiting couples with children are typically more likely to break up than less-educated married couples with children. This suggests that educational status and economics aren't the whole ball game. In 68 countries across the globe, the rise in the share of children born to cohabiting couples is associated with increased family instability for children, the report says. The effect is present even for famously progressive countries like France. In the U.S., according to the report, among children whose mothers have high education levels, 49 percent of children in cohabiting families will experience a breakup in the family, compared to just 18 percent of children whose parents are married. And even highly educated cohabiting parents in the U.S. experience higher levels of breakups (49 percent) than do less-educated married parents (26 percent).

It's important to note that this study doesn't "prove" any causal link between cohabitation and family instability. Studies that rely on correlations between different factors cannot prove a causal link between them. Perhaps parents cohabiting rather than getting married causes them to have a greater propensity to break up. Or perhaps parents with a higher propensity to end up breaking up are less likely to get married and more likely to cohabitate to begin with.

But even though the "why" is up for debate, the facts are still startling, and should cause us to pause and think. The point about educational status, in particular, is important: The vaguely pseudo-Marxist idea that our family and life outcomes are entirely driven by economics is not credible; values, norms, and institutions also matter.

Studies such as this one bolster the case that we should be protecting families through a social-legal institution that makes it harder to break up our children's lives.